Nothing - Reshiram doesn't evolve. Also, Reshiram is only in the Unova region (Black and White 1 and 2) so why is this question in Diamond, Pearl and Platinum?
Zekrom and Reshiram were originally one creature, according to legend. However you never see this creature, neither in form or a depiction of it.
Vullaby only has one evolved form which is its evolved form of Mandibuzz. Vullaby does not have a second evolved form.
The evolved form of Finneon is Lumineon.
there isn't an evolved form of pacharisu
Buneary's evolved form is Lopunny
The evolved form of Spearow is Fearow.
The evolved form of Pikachu is Raichu.
whynot is thepre evolved form
There isn't any evolved form of aerodactyl.
The evolved form of Houndour is Houndoom. It is a fire/dark type just like its pre-evolved form.
tigrerras evolved form is blade tigrerra.
The evolved form of Rhyhorn is Rhydon